Automatic volume control



June 13, 1933. w. VAN B. ROBERTS AUTOMATIC VOLUME CONTROL Filed March 50. @929 2 Sheets-Sheet l wvwnloz WALTER Vl B ROBERTS June 13, 1933.. w. VAN-B. ROBERTS AUTOMATIC VOLUME CONTROL 2 SheeLs-SheerI 2 Filed March 50, 1929 @51j his @www Patented June 13, 1933 Ui'rsD STATES reisen 4 WALTER VAN B. ROBERTS, OF PRNCETON, NEW JERSEY, ASSEGNOR TO RADIO CORPORATION OF AMERICA, A CORPORATION OF DELAWARE AUTOMATIC .VOLUME CONTROL Application led'March 30, 1929. Serial No. 351,410.

The present invention relates to volume control systems, and, more particularly, to a method of, and means for, automatically controlling the amplification volume of a re- 5 ceiving circuit.

Historically, the first receiver to `shovv selfgoverning characteristics, With reference to its amplification volume, Was the resistance coupled radio frequency amplifier employing hi gh resistance values of grid leak. In this amplifier, the radio frequency amplification decreased as signal input increased, due to the increasing negative bias on the amplifier tubes. It Will be observed that in this method the maximum Wave amplitude is What determines the radio frequency amplification.

Now, l have discovered a system for automatically controlling the yamount of amplif iication in a receiving circuit, the system utilizing the strength of a carrier Wave,

rather than the maximum Wave amplitude, whereby the radio frequency amplification is not varied by audio frequency variations of the incoming Wave amplitude, Which would reduce the effectiveness of the modulation, but is varied only by variation of carrier Wave amplitude, which maybe due to general fading effects, or `to tuning in of Y different stations.V y Accordingly, it is one of the main objects of my presentinvention to provide an automatic volume control system in a receivingl circuit, Which system compensates for fading, equalizes local and distance stations and effectively prevents the occurrence of loud blasts when a strong local station is unexpectedly tuned in, the system including the amplification of the steady direct current component of a detector plate current that 19 corresponds to the rectified carrier alone,and the utilization of the amplified direct current to control the radio'frequency amplification of the circuit.

Another important object of the invention (-3 is to provide automatic volume controlin a receiving circuit, the strength of the carrier Wave controlling the amount of amplification in the circuit, the volume control mechanism comprising a magnetron direct current amplifier adapted to amplify the rectiwhereby my'invention' may be carried into efl fiedl output of a receiving circuit, and means for Yimpressing the output of the amplifier on theradio frequencyamplifying stages of the receiving circuit. lAnother object of the invention is to provideautomatic volume control in a receiving circuit, the control mechanism comprising means for supplying biasing potential to the radio frequency amplifying stage or stages of the circuit, the last named means including an oscillator," the oscillation strength of which is controlled by variations in the carrier potentialon a detector preceding the oscillator. Y

rihe inventive featuiesfor the accomplishy ment of theseand other objects are shown herein in connection With an improved automatic volume control system which, briefly stated, includes the aniplication of the steady direct current component ofthe detector plate current that corresponds to the" rectified carrier Wave current alone.-

Y, By this means a negative potential may be obtained that changes many volts when the `carrier voltage on the detector changes a fraction of a volt. This change'k of negative potential may be applied to the grid return of one or more amplier tubes, preferably radio frequency stages, the adjustment being such that if the detector input vis less than a certain voltage m, the set operates with a maximum amplification, but if the detector input increases to an amount c, the amplification Would be reduced to zero. Thus, thev detector input cannot exceed E volts, and c--m may be made as small as desired by sufficient of the direct current yamplification mentioned above.

The novel features Which I believe to be characteristic of my invention are set forth in particularity in the' appended claims, the invention itself, however, as to botli itsorgaiiization and method of operation Willbestk be understood by reference to the following description taken in connection with the drawings in Which I have indicated diagrammatically several circuit.4 l.organizations feet.

In the drawings,

Figure l shows diagrammatically a receiving circuit embodying the automatic volume control mechanism of my invention,

Figure 2 shows a. magnetron amplifier circuit adapted to be used in place of the direct current amplifier shown in the receiving circuit in Figure 1,

Figure 8 shows a form of magnetron amplifier circuit slightly modified from that shown in Figure 2,

Figure 4L shows diagrammatically a receiving circuit, embodying another modification of a magnetron.

Figure 5 shows still another modified form of volume control, embodyino' a magnetron,

Figure 6 shows diagrammatically a receiving circuit in which automatic volume control is secured by still another modication.

Referring to the accompanying drawings, in -which like characters or reference indicate the same parts in different views, Figure l shows a receiving circuit which embodies an automatic volume control mechanism couf pled to a detector tube 3, the input circuit of the tube 3 being tuned, in the well known manner there being the usual grid condenser, shunted by a leak resistance, interposed in the grid circuit of the tube, although the grid bias type or `any type of detection may be used.

The input circuit of the tube 3 is coupled, as at M3, to the output circuit of a radio frequency amplifier stage 2, the plate circuit of the tube 2 being energized by a source B, and the input circuit of the tube being tuned, as is wel known in the art. rl`he input circuit of the tube 2 is coupled, as at M2, to the output circuit of the first radio frequency amplifier stage l, the input circuit of tube l being tuned, and the plate circuit of the tube being energized by a source B, An antenna circuit TW grounded as at G, is coupled as at M1, to the input circuit of the tube l. The filaments of the tubes l, 2 and 3 are grounded.

Across the output circuit of the tube 3 there is connected a capacity C in series with the primary coil of an audio transformer 4, the coil being connected to the filament end of the circuit and the capacity to the plate. The secondary coil of the transformer 4- is connected, in the usual manner, to any type of well known utilization means, such as phones, loud speaker or an additional audio frequency amplifier.

ln series with the plate of tube 3 there are arranged successive choke-coils L, L1, L2, capacities C1, C2, being connected across the output circuit of tube 3, it being noted that the choke coils and capacities C1, C2, form a low-pass filter permitting onlythe steady direct current component of the plate current of the detector 3 to flow through a high resistance It connected in series with a source of plate potential B, both resistance and source being connected in series with the choke coils.

It should be noted that the steady direct current component of the detector plate current corresponds to the rectified carrier alone, and by means of the resistance R a negative potential may be obtained that'changes several volts when the carrier voltage on the detector 3 changes a fraction of a volt. As stated above, between points A, B of the output circuit ofthe detector 3, a high resistance R is inserted to obtain voltage input for a simple direct current amplifier.

rlhis amplifier includes tube 6, the grid of which is connected by an adjustable means 5 to the source B, and the plate circuit of which is energized by a source B. A second high resistance l?.1V is connected in series with the plate or" tube 6, and potential is adjustably secured therefrom by a variable member 7, the latter being connected by a line 8 to the input circuits of each of the radio frequency amplifier stages.

The receiving circuit, as shown, is operated in the usual manner, the input stages of the tubes l, 2 and 3 preferably being uni-ccntrolled, and the audio current bein continuously utilized through the audio frequency transformer 4l. The direct current due to the carrier wave, is employed for automatically controlling the amount of amplification secured in the radio frequency amplifier stages'. The operation `of the volume control mechanism will be apparent from the drawing and description as given.

ft is to be understood that the circuit elements are so adjusted thatl if the detector input is less than a certain voltage m, the set operates with a maximum amplification, but if the detector input is increased to an amount e, the amplification would be reduced to zero. Thus, if the signals are strong enough to be brought up to value m by maximum amplification, the detector input can not vary by more than e-m volts, and, of course, this variation may be made as small asdesired by sufiicient of the direct current amplification. Y Y

When strong signals are received the direct current in the plate circuit of the detector 3 is decreased. As a result of this the output of the direct current amplifier 6 is increased causing an increased current flow through resistance R1. The increased current flow through resistance R1 causes the point A thereon to become relatively more negative, and from this there follows an increased negative bias on the grids of amplifiers i and 2 which in turn cuts down their amplification.

Conversely, when the incoming signal energy diminishes in value then the -current flowing through the resistance lll decreases and the gid bias on tubes 1 and 2 becomes less negative, By virtue of the latter fact the amplification of tubes 1 and 2 of the incoming.,.signal ii-1cr'eas`es,fand,'` hence, in the utilization means there is maintained Aa signal substantially constantfintensity, in other words, it will be seen l have devised,ca metliod for maintaining signal amplication-V betweenk predetermined limits of intens-ity, whichl system involves the amplification of sniall,.fariations in the direct current component of the plate current of the detector of a receiving circuit; which va liations arerengendered by corresponding variations inthe strength of the incoming carrier wave,'tlie amplified variations being adjusted to control the radio frequency amplifying stages, of the receiving circuit by biasing the grid of each amplifying stage in such a manner that the amplifying stages operate within the predetermined limits.

instead of the direct current amplifier shown in Figure l a-direct current amplifier, employing magnetrons, may be utilized as shown inFigure 2V. Between points A and B of the receiving circuit shown in Figure l, the circuit members preceding these two points being omitted for the salie of sim# plicity, the magnetron field coil ll isv connected.- rlhe source B is used to adjust the field coil ll to its critical value by means of an ,adjustment member 11'.'V The magnetron diode 9 has-its plate energized by a source B, yanda second field coil l2 .is connected in series withv the source B .The latter coil i2controls the action of a second magnetron 10, the output current of .this final magnetron iiowing Ythrough a res istance R1 arranged in its plate circuit, the

` control voltage being taken olf by .an adjustable member 7 from the resistance R1. As in Figure l, the potential from the resistance B., is .led through a line S to the grids of the amplifying stages of the receiving circuit.

In Figure 3 there is shown a magnetron amplifier, modified from the amplifier shown in Figure 2, in that, instead of using the source B for adjusting the field coil ll to its critical v.alue,another field coil 13, connected in series with a rheostat 15 and a source of potentiallt, adjusts the field to its critical value. rlhe amplifier in Figure 3 functions in the receiving"v circuit in the same manner as described heretofore.

In Figure t, there is shown a receiving circuit of the same type shown in Figure l, employing a magnetron amplifier in which a magnetron field coil 16 is connected between points A, B, the critical value ofthe field coil being adjusted by afsecondiield coil i8 connected in series with a rliecstat i9 and a source of potential 20, as noted in Figure 3. The magnetron diode 17. has connected in seriesY with its plate circuit a resistance R1A in series with a source B of potential for the diode plate.

rlhe magnetron am oliiier outut is impressed uponthe plate circuits of the' amplifier stagesl, 2 by means Vof'connecting lines 23,24. It will be observed, that in this type of'circuit, a change of plate resistance B1 of the magnetron 17 affects the'plate voltage ofthe radio frequency amplifiers l, 2.

l/Vhen the magnetron resistance falls from nearly infinity to ynearly Zero, the plate voltages of the tubes 1,2 drop from approizimately the value of the potential of source B to nearly Zero. if thel operating point is at the knee of asharp-cut ofi'y magnetron the reduction of the plate potential would be very rapid.

l/Vhen only a single magnetron is used, vol# inne may be determined by the adjuster 19 of theield. if this isbrought awayfrom the critical kvalue no control would be effected..

lf brought onto the steep part of the curve, the amplification would be reduced even for weak signals, and the governing action will be stiifest.

Another modification ofy receiving circuit employing a magnetron amplilier for automatic volume control, is shown in Figure '5. In this circuit, the circuit elements are the same as in Figure l, but a magnetron field coil 30 is connected between points A, B,y a magnetron diode 29 having a source B7 in its plate circuit, the negative terminalof the source being connected to the iilament of amplifier stage 25 by a line 2l, the other terminal of the diode 29 being connected by a line 32 in the plate circuit of the tube 25.

As in Figure l, the audio current from Vthe detector is utilized in any well known Jforni of utilization means, and the direct currentv passed through a low-pass filter. The critical value of the field coil 3VO is controlled by-a second field coil `28'having connected in Vries therewith a rlieostat 26 and source as shown in Figure 3. In this case magnetron. 29 varies the amplication ortube 25 by rangement, which output being rectified and smoothed out provides potential for the grids of the radio frequency f mplifier stages of the circuit. The output of a master oscillator is impressed upon the grid circuit of the tube 33 through a coupling Mi, the grid vcircuit beingconnected to one end or" the resistance R.

V- The plate of tube 33 is ener,a lby a source Bv and is connected tothe other end of the resistance R. The plate circuit ofthe tube 33 is coupled through a resonant circuit 34 to a crystal rectifier 35, the rectified output being filtered Vthrough, al filter ineniber L3, C3, C4 there being a resistance R1 connected across the filter member, whereby after amplification and rectification the oscillations are impressed upon the grid circuit of the radio frequency amplifier stages through lines 36 and 37. In this way the amplification of signal energy is maintained between. predetermined limits.

i While I have indicated and described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organization shown and described, but that many more modifications in the circuit arrangements, well as in the apparatus employed, may be used without departing from the scope of my invention as set forth in the appended claims.

'What I claim is:

l. An automatic volume control for a receiving circuit comprising means for collecting signal energy, signal enel` amplifying means, a detector coupled to said amplifying means, a source of detector anode current,

' a magnetron direct current amplifier including a field coil connected to said source to amplify the direct current component of the detector signal plate current, andnieans for impressing the output of the magnetron amplifier on the signal energy amplfying means. 2. An automatic volume co l for a re ceiving circuit comprising means for collegeting signal energy, radio frequency amplifying means, a detecting tube, a source of detector anode current, a magnetron :nnplin fier including a field coil connected to said source to amplify the direct current component of the detector .pls i means for adjusting the l .ld coil to its value and means, including a resistance, for impressing the output of the magnetron amplifier on the radio frequency amplifying means.

3. In combination, in a radio receiver, an antenna, a radio frequency amplifier, a detector stage including an electron discharge tube, an audio frequency transformer primary in the anode circuit of the tube, a direct current blocking condenser connected between the primary and the detector anode, a source of current for said anode', a path of high impedance to pulsating current connected between said anode and the positive side of said source, a high impedance connected between said source and the low potential side of said primary, a direct current amplifier connected across said impedance, and means for controlling the gain of the radio frequency amplifier with the output of said direct current amplifier. v

4:. In combination, in a radio receiver, an antenna, a. multi-stage radio frequency amplifier, a detector stage including an electron discharge tube, an audio frequency transformer primary in vthe anode circuit of the tube, a direct current blocking condenser con#V nected in series between the primary and the detector anode, a source of current for said anode, a path of high imp-edance to pulsating current connected between said anode and the positive side of said source, a high impedance connected between said source and the low potential side of said primary, a direct current amplifier connected across said impedance, and means for controllingthe gain of the radio frequency amplifier with the out-put of said direct current amplifier.

5. In combination, in a radio receiver, Van

antenna,a radio frequency amplifier, a de# tector stage including an electron discharge tube, an audio frequency transformer primary in the anode circuit of the tube, a direct current blocking condenser connected between the primary and the detector anode, a source of current for said anode, a path of high impedance to pulsating current connected in series between said'anode and the positive side of said source, a high impedance vcomiccted in series between said source and mary in the anode circuit of the tube, a di rect current. blocking condenser connected between the primary and the detector anode, a source of current for said anode, a path of high impedance to pulsating current connected between said anode and the positive side of said source, a high impedance con-` nected between the negative side of said source and the low potential side of said primary, a direct current amplifier connected across said impedance, and means for controlling the gain of the radio frequency amplifier with the output of said direct current amplifier.

7. In combination, in a radio receiver, an

antenna, a nml-ti-stagefradio frequency am-V plifier, a detector stage including an electron discharge tube, an audio frequency transformer primary in the anode circuit of the tube, a direct current blocking condenser connected in series between the primary and the detector anode, a source of current for said anode, a path of high impedance to puls sating current connected in seriesbetween said anode and the positive side of said source, high impedance connected in series between the negative side of said sourcey and the low potential side of said primary, a direct current amplier connected across said impedance and means for controlling the gain of the radio frequency amplifier with the output of said direct current amplifier.

lOO

lio

' 8. An automatic lgain control system for a radio receiver including "anv antenna, a radio` frequency amplifier, ya "detector tube, an audio frequency transformer for coupling the detector anode circuity to ya 'succeeding audio frequ @icy energy utilization means, a source ofenergizing current for the detector anode, the transformer primary being connected With saiddetector anode, a device` having a high impedance to direct current and a low impedanceito pulsating current connected in 'series between said detector anode andthe higlipotential terminal lof said frequency energy utilization means, a sourcek of energizing current for the detector anode, the transformer primary being connected with said detector anode, means for blocking the flow of current from said source through said transformer primary, means for connecting said source to said detector anode, an amplifier to amplify the direc-tv current component of the detector signal anode current,

and means for controlling the gain of said radio frequency amplifier With the output of said direct current amplifier.

10. 15in automatic gain control system for a radio receiver including an antenna, a radio frequency amplifier, a detector tube, an audio frequency transformer for coupling the detector anode circuit to a succeeding audio frequency energy utilization means, a source of energizing current for the detector anode, the transformer primary being connected with said detector anode, a device having a high impedance to direct current and a loW impedance to pulsating current connected in series between said detector anode and the iigh potential terminal of said primary, a low pass filter between the detector output circuit and said source, means for connecting said source to said detector anode, an amplilier to amplify the direct current component of the detector signal anode current, and means for controlling the gain of said radio frequency amplilier with the output of said direct current amplifier.

11. An automatic gain control system for a radio receiver including an antenna, a radio frequency amplifier, detector tube, an

audio frequency transformer for coupling the detect node circuit to a succeeding audio frequency energy utilization means, a

source of energizing current for'the detector Vthe' eain of said radio anode, lthe transformer primary being connected with said detector anode, a device having a high impedanceto direct current and a low impedance to pulsating current connected in series between said detectoranode and the high potential terminal of said primary, means for vconnecting said source to said detector anode, an amplifier to amplify the direct current component of the detector signal anode current, and means for controlling frequency amplifier with the output of said direct current amplifier, said direct current amplifier comprising a source of oscillations, means for impressing-said oscillations upon the input circuit of an amplifier tube, means for coupling said `latter input circuit to the detector outputcircuit, and means for rectifying the output of said oscillation amplifying means.

12. In a radio receiver, a radio frequency amplifier stage including a tube, a detector stage including a tube, a source of direct current for the detector ytube anode,y means in the detector anode circuit for coupling the same to an audio frequency signal utilization means, means for amplifying the direct currentfoutput. of the detector tube comprising a magnetron diode, a field coil forV the diode connected to the said current source in the detectorfanode circuit, and a gain lcontrol connection between said diode and the radio frequency amplifier.

13.r In a radio receiver, a radio frequency amplifier stage including La tube, a detector stage including a tube, a source of direct cur-` rent for the detectortube anode, means in the detector anode circuit for coupling the same to an audio frequency signal utilization means, means for amplifying the directeurrent outputof the 'detector tubel comprisingv a magnetron diode, a field coil forthe diode connected to the said current source in the detector anode circuit, and a gain control connection including a resist-ance across the diode electrodes, between said diode and the radio frequency amplifier. i

14. An automatic gain control system for a radio receiver including an antenna, aradio frequency amplifier. a detector tube, an audio frequency transformer for coupling the detector anode circuit to a succeeding audio4 frequency energy utilization means, a sourcel of energizing current for the detector anode, the transformer primary being connected. withv said detector anode, `means for` blocking the flow of current from'said source through said transformer primary, means for c'i'inne'cting` said source to said detector anode, an amplifier to'amplifv the direct current component of the detector signal anode current, said amplifier consistingof a magnetrondiode having a field coil connected in said detectorfanode circuit to said detector anode energizing'current source, and means for controlling the gain'of said radiov freilo izo

ist

quency amplifier with the output of said direct current amplifier.

15. 1n a radio receiver. a radio frequency amplifier stage including a tube, a detector stage including a tube, a sour-ce of direct current for tie detetor tube anode, means in the detector anode circuit for coupling the same to an audio frequency signal utilization means, means for amplifying the direct current output of the detector tube comprising a magnetron diode a field coil for the diode connected to the said current source in the detector anode circuit, and a gain control connection between said diode and a cold electrode of the radio frequency amplifier tube.

16. 1n a radio receiver, a radio frequency amplier stage including a tube, a Adetector stage including a tube, a source of direct current for the detector tube anode, means in the detector anode circuit for coupling the same to an audio frequency signal utilization means, means for amplifying the direct current output of the detector tube comprising a magnetron diode, a field coil for the diode connected to the said current source in the detector anode circuit, and a gain control connection between said diode and a positive cold electrode of the radio frequency amplifier tube.

17 ln a radio receiver, a. radio frequency amplifier stage including a tube, a detector stage including a tube, a source of direct current for the detector tube anode, means in the. detector anode circuit for coupling the same to an audio frequency signal utilization means, means for amplifying the direct current output of the detector tube comprising a magnetron diode, a field coil for the diode connected to the said current source in the detector anode circuit, said diode being connected'in series in a cold electrode circuit of said amplifier tube to provide a gain control circuit.

18. In a radio receiver, a radio frequency stage including a tube, a source of direct current for the detector tube anode, means in the detector anode circuit for coupling the same to an audio frequency signal utilization means, means for amplifying the direct current output of the detector tube comprising a magnetron diode, a field coil for the diode connected to the said current source in the detector anode circuit, said diode being connectedin series in a positive cold electrode circuit of said amplifier tube to provide a gain control circuit.

19o in a radio receiver, a radio frequency amplifier stage including a` tube, a detector j stage including` a tube, a source of direct current for the detector tube anode, means in the detector anode circuit for coupling the same to an audio frequency signal utilization means, means for amplifying the direct current output of the detector tube comprising a magnetron diode, a eld coil for the diode connected to the saidA current source in the detector anode circuit, and a gain control connection between said diode and the radio frequency amplifier and means for controlling the Vaction of said vmagnetron diode.

20. ln a radio receiver of the type comprising a radio frequency amplifier, including a tube, having a resonant input circuit tuned to a desired signal frequency, a detector, including a tube, provided with an input circuit coupled to the amplifier to receive signal energy therefrom to be rectied, and' means for utilizing the audio frequency component of rectied signal energy, an automatic volume control arrangement comprising a magnetron diode, a field coil for said diode con-- nected to the said detector and disposed in the path of flow of the direct current component of the rectified signal energy, and a direct current connection between said diode and a cold' electrode of said amplifier tube for adjusting the potential of said cold electrode in response to variations of said direct current component flow through said field coil.

yVVAL'IER VAN B. ROBERTS. 

